This invention relates generally to chairs and, more specifically, to tilt back chairs and mechanisms for controlling the tilting of the back of a tilt back chair.
Tilt back chairs, wherein the back of the chairxe2x80x94or the back and the seat of the chairxe2x80x94tilt rearwardly with respect to the base of the chair, have become very popular. Tilt back chairs are especially popular for use as office chairs and conference room chairs.
Traditionally, the resistance to the tilting of the back of a tilt back chair is controlled by one or more coil springs. Recently, tilt back chairs have been designed using an elastomeric spring instead of coil springs. The use of elastomeric springs is believed by many to provide a smoother and more easily controlled tilt to the back of a tilt back chair. One such tilt back chair using an elastomeric spring is disclosed in U.S. Pat. No. 5,772,282, the entirety of which is incorporated herein by this reference.
Unfortunately, the use of an elastomeric spring in the tilt back chair disclosed in U.S. Pat. No. 5,772,282 is not wholly satisfactory. One problem with such a chair has to do with manually increasing the pretension on the elastomeric spring. In the chair taught in U.S. Pat. No. 5,772,282, manually increasing the pretension on the elastomeric spring becomes increasingly difficult as the pretension on the spring increases.
Accordingly, there is a need for a tilt back chair using an elastomeric spring which avoids the aforementioned problems in the prior art.
The invention satisfies this need. The invention is a tilt rate adjustment mechanism for use in a tilt back chair having a base, a seat and a back. The tilt rate adjustment mechanism is adapted to adjust the amount of force required to tilt the back of the chair, or the back and the seat of the chair, relative to the base of the chair.
In the invention, the tilt rate adjustment mechanism comprises an adjustable torsion spring, a tilt rate adjustment actuator and an actuator movement mechanism. The torsion spring is mounted on a torsion spring shaft. The torsion spring is operatively attached to the back of the tilt back chair such that the rearward tilting of the back is resisted by the tension of the torsion spring. The torsion spring has an adjustment lever for adjusting the tension on the torsion spring. The adjustment lever has a proximal end, a central portion and a distal end. The proximal end of the adjustment lever is rotatable about the torsion spring shaft between a minimum tension position, wherein the torsion spring resists the tilting of the chair back with minimum tension, and a maximum tension position, wherein the tension spring resists the tilting of the chair back with maximum tension.
The tilt rate adjustment actuator is disposed in contact with the adjustment lever such that the movement of the adjustment actuator causes movement of the adjustment lever. The adjustment actuator is moveable between (i) a first actuator position wherein the actuator is proximal to the torsion spring and the adjustment lever is in the minimum tension position, and (ii) a second actuator position wherein the actuator is distal from the torsion spring and the adjustment lever is in the maximum tension position.
Finally, the actuator movement mechanism is adapted to alternatively move the actuator back and forth between the first actuator position and the second actuator position.
In a typical, but not required, embodiment, the adjustable torsion spring is an elastomeric torsion spring.
In one embodiment of the invention, the adjustable torsion spring is operably attached to both the back and the seat of the tilt back chair such that the rearward tilting of both the back and the seat of the chair is resisted by the tension of the torsion spring.